Tunable photonic devices by 3D laser printing of liquid crystal elastomers
4D printing of liquid crystal elastomer (LCE) based on femtosecond laser two-photon polymerization (TPP) enables fabricating tunable photonic devices. 4D printing involves the time axis as a 4th dimension to provide the capability of shape transformation to 3D printed objects by external stimuli such as temperature, optical excitation, or electric/magnetic fields. This paper demonstrates that the 3D structures of LCE printed by optimized TPP can reversibly change their shapes by changes in temperature due to perturbation of the directional order of rod-shaped mesogens in the polymeric network. This unique characteristic was applied to fabricate tunable photonic elements, specifically, whispering gallery mode (WGM) resonators with a high-quality factor and a wide, precise tunability. Importantly, the 3D printed LCE can simultaneously change both the effective refractive index and the cavity’s radius by the stimuli, resulting in achieving strong wavelength shifts for the WGM resonators. Thus, the technique developed in this paper will establish a platform to produce complex architectures of tunable photonic elements.